(1) Summary of the Invention
The present invention relates to a method for producing sugar beet plants (Beta vulgaris L.) which are resistant to both imidazolinone and sulfonylurea herbicides used for weed control. In particular, the present invention relates to sugar beet plants derived from a susceptible sugar beet by mutation of a gene encoding acetolactate synthase (ALS) also known as acetohydroxyacid synthase (AHAS) using the herbicides sequentially with cells in a culture medium.
(2) Description of Related Art
The prior art has described the genetic alteration of the acetolactate synthase gene by recombinant means as shown by U.S. Pat. Nos. 5,013,659; 5,141,870 and 5,378,824. This type of modification in sugar beet plants is shown by Example IV of the '824 patent. The results were less than satisfactory in producing plants which breed true for the herbicide resistance.
Saunders et al. in Crop Science 32:1357-1360 (1992) also describe the production of the sugar beet plant (CR1-B) which is resistant to sulfonylureas from the susceptible self-fertile clone (REL-1) by selection for mutant cells in a culture medium containing the herbicide. Various resistant plants were produced and cross-bred. Hart et al. (Weed Science 40378-383 (1992) and 41:317-324 (1993)) further characterized the resistant line and determined the resistance was due to altered ALS activity and showed no cross resistance to other ALS-inhibiting herbicides, and was coded for by a single, semidominant gene.
There are no publications describing imidazolinone resistance obtained by modifying ALS in sugar beet plants. There is no description in the literature of plants which are resistant to both imidazolinone and sulfonylurea herbicides. Various corn lines with imidazolinone resistance have been developed as described by Newhouse et al. Theoretical and Applied Genetics 83:65-70 (1991).
A commercial route to crop protection is the use of clinical "safeners" such as described in European Patent No. 375,875. This method introduces another chemical into the soil. The preferred method is to develop sugar beet plants which are resistant to the imidazolinone and sulfonylurea herbicides.